File content as of revision 0:dc2c526097d2:

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#include "mbed.h"
#include "bcdutil.h"


static struct tm __t;
static char __rtc_data[20];

unsigned int bin2bcd(unsigned int n)
{
    unsigned int bcd=0;
    unsigned int base=0;

    while (n>0) {
        bcd |= (n%10)<<base;
        base += 4;
        n /= 10;
    }
    return bcd;
}

unsigned char bcd2bin(unsigned char bcd)
{
//    return 10*((bcd>>4)&0xF) + bcd&0xF;   // not good. don't know why.
    unsigned char temp = bcd & 0x0F;
    while (bcd>=0x10) {
        temp += 10;
        bcd -= 0x10;
    }
    return temp;
}

char*
tm2rtc(struct tm* _t)          // tm -> rtc(BCD)
{
    __rtc_data[2] = bin2bcd(_t->tm_sec);
    __rtc_data[3] = bin2bcd(_t->tm_min);
    __rtc_data[4] = bin2bcd(_t->tm_hour);
    __rtc_data[5] = bin2bcd(_t->tm_mday);
    __rtc_data[7] = bin2bcd(_t->tm_mon);
    __rtc_data[8] = bin2bcd(_t->tm_year-100);
    return __rtc_data;
}

struct tm*
rtc2tm(char* _bcd) {  // rtc(BCD) -> tm
    __t.tm_sec = bcd2bin(_bcd[2]&0x7F);      // 0-59
    __t.tm_min = bcd2bin(_bcd[3]&0x7F);      // 0-59
    __t.tm_hour= bcd2bin(_bcd[4]&0x3F);      // 0-23
    __t.tm_mday= bcd2bin(_bcd[5]&0x3F);      // 1-31
    __t.tm_mon = bcd2bin(_bcd[7]&0x1F);      // 0-11
    __t.tm_year= bcd2bin(_bcd[8])+100;  // year since 1900
    return &__t;
}